The present invention generally relates to pen input devices, and more particularly to a pen input device for inputting information such as graphics and characters to a computer or the like.
Conventionally, an input device for inputting information such as graphics and characters to a computer or the like can generally be divided into a first input device which uses a mouse, and a second input device which uses a pressure-sensitive (or contact type) pen tablet.
Presently, the first input device which uses the mouse is popularly used for inputting information to a computer aided design (CAD) system. According to this first input device, the mouse is placed on the tablet and moved manually by the operator, so as to rotate a ball which is provided in the mouse by the friction between the ball and the tablet. The magnitudes of the movement in the vertical and horizontal directions are detected depending on the rotation quantity of the ball, and the detected magnitudes are converted into an electrical signal before being input to the computer. The tablet may take an arbitrary form as long as the surface of the tablet is sufficiently large for enabling rotation of the ball of the mouse when the mouse is moved.
The first input device has a relatively simple construction, and inexpensive first input devices have been produced.
When displaying the position of the mouse on the tablet on a display unit such as a cathode ray tube (CRT) and a liquid crystal display (LCD) by a computer based on the input signal from the first input device, the movement of a point (hereinafter referred to as a cursor) which indicates the position of the mouse on the display unit corresponds one-to-one to the movement of the mouse. Hence, the operator can indirectly confirm the movement of the mouse, that is, the movement of the operator's hand, by monitoring the movement of the cursor displayed on the display unit. As a result, the cursor can be moved in an arbitrary direction in a simple manner, and an arbitrary graphic can be drawn at an arbitrary position on the display unit. In addition, since the movement of the mouse is input to the computer only while the mouse makes contact with the tablet, the cursor can be moved within the entire display area of the display unit to draw the graphic or the like, even if the tablet used is smaller than the display area of the display unit, by repeatedly moving the mouse in the same direction.
On the other hand, the second input device detects the pressure at the tip end of an input pen using a sensor which is mounted on the tablet. Hence, when drawing the graphics or characters on the tablet by the input pen, the locus of the input pen is detected as information which is related to the absolute position on the tablet.
Furthermore, a third input device has recently been proposed in "Information Tool Classified Catalog '92.2" by Sony Corporation. According to this third input device, the device which displays the locus of the input pen and the tablet are stacked. As a result, the locus of the tip of the input pen can be displayed at the same position. In other words, the graphics and characters can be input by the input pen in a sense relatively close to the case where the graphics and characters are written on a paper by a pencil.
However, the first, second and third input devices also have the following drawbacks.
First, according to the first input device, the position of the mouse on the tablet and the position of the cursor on the display unit do not correspond one-to-one. In addition, according to some experts, it is difficult to draw graphics and characters by the mouse when using a CAD or desk top publishing (DTP) software. More particularly, it is simple to draw a large circle or a large character which take up almost the entire display area of the display unit, however, it is difficult to draw small graphics and small characters. It may be regarded that these problems are mainly caused by the shape of the mouse. As may be seen when the mouse is moved to draw a small character, the mouse must be moved by holding the mouse by the entire palm of the operator's hand, and it is for this reason that the mouse cannot be accurately controlled to make fine movements, thereby making accurate input of fine graphics and characters difficult by the mouse.
In addition, drawing a graphic or the like on a paper by a pencil and drawing the graphic or the like by the mouse are quite different in nature. In other words, when drawing the graphic or the like on the paper by the pencil, the pencil frequently repeats contact and separation with respect to the paper. More particularly, the pencil makes contact with the paper when drawing a line, for example, and the pencil can be moved to a different position on the paper by separating the pencil from the paper if no line is to be drawn. On the other hand, in the case of the mouse, the mouse must constantly be in contact with the tablet while supplying the movement of the mouse to the computer. For this reason, a switch is turned ON/OFF to specify whether or not the cursor locus is to be drawn and displayed on the display unit. Therefore, this ON/OFF control of the switch makes the operation of the mouse complex and unsuited for inputting the graphics or the like at a high speed.
Second, the second input device draws the graphics or characters on the tablet by the input pen and detects the locus of the input pen as the information related to the absolute position on the tablet. Hence, when displaying the drawn graphics or characters on the display unit, the position of the cursor displayed on the display unit and the position of the tip of the input pen on the tablet correspond one-to-one, and the drawn graphics or characters can be input as they as to the computer. However, in a case where the tablet and the display unit are separated, the operator must confirm the movement of the input pen by monitoring the movement of the cursor displayed on the display unit. And, in order to do this, the tip of the input pen must constantly be in contact with the tablet. As a result, a problem similar to that encountered in the first input device also exists in the second input device, in that it is necessary to specify whether or not the cursor locus is to be drawn and displayed on the display unit by contacting or separating the tip of the input pen with respect to the tablet.
Third, according to the third input device, the construction is complex and it is difficult to realize a large device. On the other hand, in the case of an electronic pocketbook for inputting characters, for example, it is only possible to input a very limited number of characters, and is unsuited for drawing graphics or the like on a large display unit.
Therefore, there are demands to realize an input device which can overcome the above described problems of the first, second and third input devices.